The present disclosure relates to a signal transmission system, a signal processing device, an electronic device, reference signal transmitting device, reference signal receiving device, and a signal transmission method. More particularly, the present disclosure relates to a mechanism of performing signal processing using a reference signal (reference clock). For example, the present disclosure relates to handling of a local oscillation signal when communication is performed between a plurality of radio communicating devices.
There is a case of performing signal processing using a reference signal (reference clock) in an electronic device. In this case, when a plurality of circuit functional parts need the reference signal, there is a problem of how to provide the reference signal to each position (supply the reference signal to each circuit functional part).
For example, when a plurality of chips (semiconductor integrated circuits) that need a reference signal generated by a crystal oscillator or the like as a clock for a digital circuit or a reference for a synthesizer are necessary within an electronic device, providing each chip with an oscillator is considered. In this case, however, interference between a plurality of oscillation signals occurs, and thus a measure against noise is necessary.
When a reference signal is shared, and the reference signal is transmitted to each position, interference is eliminated, and thus the need for a measure against noise is obviated. In this case, however, wiring for sharing the reference signal and transmitting the reference signal to each position becomes necessary, there is a fear of an increase in effect of signal distortion due to reflection and the like, and a problem of spurious radiation also occurs when the level of the reference signal is increased. For example, LVDS (Low Voltage Differential Signaling) is known as a method for realizing high-speed signal transmission between electronic devices arranged at a relatively short distance (within a few centimeters to a few ten centimeters, for example) from each other or within an electronic device, and transmitting the reference signal by applying LVDS is considered. However, when the frequency of the reference signal is increased, LVDS is reaching a limit because of the problems of signal distortion, spurious radiation and the like.
In addition, when communication using synchronous detection is performed in a field of communication, the respective local oscillation frequencies of a transmitting device and a receiving device (also referred to collectively as a transmitter-receiver) have to be synchronized with each other. For this synchronization, the local oscillation signals may be generated on the basis of a common reference signal. In this case, although the local oscillation frequencies are synchronized with each other, wiring for sharing the reference signal and transmitting the reference signal to the transmitting device and the receiving device becomes necessary, and a problem of radiation also occurs when the level of the reference signal is increased, as described above. As another method, synchronization may be achieved by a received baseband signal while local oscillation signals not synchronized with each other are used. However, the method increases a circuit scale and power consumption.
In addition, Japanese Patent Laid-Open No. 2003-244016 (referred to as Patent Document 1 hereinafter) proposes a system in which a local oscillation signal in a millimeter wave band is transmitted, and in which transmission and reception are performed after an intermediate frequency band signal is raised to the millimeter wave band using the common local oscillation signal received by each communication chip. However, this mechanism is a system limited to communication using intermediate frequency band signals, and a signal processing circuit for generating and processing the intermediate frequency band signals is necessary. In addition, because the local oscillation signal itself is shared, one kind of frequency can be used as the local oscillation signal.